Floor sanding machines according to the preamble to the first patent claim have already been familiar for decades and are proven in service. A good example of the early recognition of such technology and its advantages can be found in patent number U.S. Pat. No. 835,631 dating from the year 1905.
The re-examination of this technology towards the end of the twentieth century led to an abundance of patent applications followed by the granting of patents. Accordingly, it appears appropriate to the applicant to submit patent applications in respect of inventions made in the course of research and considered to be relevant: U.S. Pat. No. 6,783,447; U.S. Pat. No. 5,637,032; U.S. Pat. No. 6,540,596 and U.S. Pat. No. 6,331,138. This list is not exhaustive, although it contains the specifications that are considered important.
The present specifications reveal clear disadvantages. In the case of U.S. Pat. No. 6,783,447, for example, the fact that three belt drives are used is disadvantageous, due to the requirement for more space, as a consequence of which the device is ungainly. In addition, the gear mechanism is arranged eccentrically as additional weight and as such generates an imbalance in the device that is disadvantageous for the sanding process. Imbalance in a device of this kind always produces a one-sided application of force to the sanding tools, which manifests itself when operating such a device in the machine “drifting to one side” and having to be restrained against this tendency to “swing out”. A further disadvantage associated with the static, eccentric loading of the sanding tools relates to the sanding process. Depending on their individual position, the sanding tools are subjected to more or less weight, which also reveals itself in an uneven sanding pattern. These disadvantages are also exhibited by U.S. Pat. No. 6,540,596, which operates with two drive motors.
A different situation applies in the case of U.S. Pat. No. 5,637,032. The flat belt, which is depicted in FIG. 2b as passing around both the large pulley and the small tool driving pulleys, is under high tension. Its replacement presents a very considerable risk of accident to the persons involved. A further disadvantage, which is compensated for in part by an increased tension in this particular flat belt, is the exceptionally small angle of belt contact of the sanding tool drive shafts 8c. 
Devices that are constructed according to the design principles described above are available on the market and are also sold. They are affected by the shortcomings outlined above.
The present invention has as its object the improvement of a floor sanding device of the kind mentioned by way of introduction, in such a way that the advantages of the previously disclosed floor sanding machines are retained, but that the device is more easily operated, the mechanical drive components are reliably protected against contamination by dirt, and repair and maintenance operations can be carried out simply and without the risk of accident to the personnel.
This object is achieved by a floor sanding machine having the characterizing features of Patent claim 1. Further characterizing features in accordance with the invention can be appreciated from the dependent claims, and their advantages are explained in the following description.
The figures depict preferred proposed embodiments, which are explained as examples in the following description.